bitmanipulation: fix undefined behavior in bit shift in getbe32
OSS-Fuzz caught this in its ubsan mode[0]. I'm not worried about a
security issue here because in practice this should work out the way
we naively expected, we're just making things explicit to the
compiler with the casts.
0: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=8876
Differential Revision: https://phab.mercurial-scm.org/D3729
--- a/contrib/fuzz/mpatch_corpus.py Wed Jun 13 21:58:42 2018 +0900
+++ b/contrib/fuzz/mpatch_corpus.py Wed Jun 13 10:24:44 2018 -0400
@@ -78,6 +78,10 @@
zf.writestr(
"mpatch_decode_old_overread", "\x02\x00\x00\x00\x02\x00\x00\x00"
)
+ # https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=8876
+ zf.writestr(
+ "mpatch_ossfuzz_getbe32_ubsan",
+ "\x02\x00\x00\x00\x0c \xff\xff\xff\xff ")
zf.writestr(
"mpatch_apply_over_memcpy",
'\x13\x01\x00\x05\xd0\x00\x00\x00\x00\x00\x00\x00\x00\n \x00\x00\x00'
--- a/mercurial/bitmanipulation.h Wed Jun 13 21:58:42 2018 +0900
+++ b/mercurial/bitmanipulation.h Wed Jun 13 10:24:44 2018 -0400
@@ -9,7 +9,8 @@
{
const unsigned char *d = (const unsigned char *)c;
- return ((d[0] << 24) | (d[1] << 16) | (d[2] << 8) | (d[3]));
+ return ((((uint32_t)d[0]) << 24) | (((uint32_t)d[1]) << 16) |
+ (((uint32_t)d[2]) << 8) | (d[3]));
}
static inline int16_t getbeint16(const char *c)